In this paper,the effect of optical fiber loss on temperature er ror of Raman distributed optical fiber sensor is analyzed by using the temperature demodulation principle.The errors are experimentally investigated by contemporarily measuring the temperatures of two temperature control boxes at different positions of a fiber.A law is found that when the temperat ure of optical fiber varies between 20℃ and 100℃,the effect of the fiber per unit length on the additional temperature error produced by the loss of opti cal fibers is not only proportional to the temperature of the optical fibers,but also to the length of optical fibers.Furthermore,temperatur e error is calibrated based on this finding.The experimental results show that the additional temperature error of a 700m long optical fiber out of a 2k m total length controlled by the heater has dropped down from 4.09℃ to no more than 0.47℃.